Visceral Fat May Raise Men's Fracture Risk

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Note that this study was published as an abstract and presented at a conference. These data and conclusions should be considered to be preliminary until published in a peer-reviewed journal.

A small study found visceral fat was associated with decreased bone strength in obese men compared with those with the same body mass index who had less visceral fat.

Note that thigh muscle area was associated with both increased bone stiffness and failure load -- measures of bone strength -- while visceral fat was inversely correlated.

CHICAGO -- Having more visceral fat -- the kind that collects around the internal organs of the abdomen, rather than just beneath the skin -- appears to put men at a higher risk of bone loss, researchers said here.

In a single-center study, younger, heavier men with more visceral fat had lower failure load and stiffness -- measures of bone strength -- compared with those who had less visceral fat, despite having a comparable body mass index (P=0.04 and P=0.03, respectively), Miriam Bredella, MD, of Massachusetts General Hospital, and colleagues reported during a press briefing at the Radiological Society of North America meeting here.

"Young, obese men with a large amount of visceral fat have weaker bones, putting these young men at risk of not only heart disease and diabetes, but also for developing fractures," Bredella said during the briefing.

She noted that most studies on osteoporosis have focused on women, as men -- especially obese men -- have been thought to be protected against bone loss.

But differences in the way the body stores fat may yield clues about other metabolic issues, like bone growth and loss, Bredella said.

So she and her colleagues assessed 35 obese men, mean age 34, who had a mean body mass index (BMI) of 36.5. All of them had a CT scan of the abdomen and of the thigh in order to assess fat and muscle mass.

The men also underwent a high-resolution CT of the forearm, known as finite element analysis (FEA), to assess mechanical properties of the bone, including stiffness and failure load. This type of scan, Bredella said, is commonly used in engineering to test the strength of materials, particularly those used in cars and airplanes.

Overall, the researchers found that men who had more visceral fat had lower values on measures of bone strength than those who had less visceral fat, despite comparable BMIs.

Specifically, men with high levels of visceral fat had significant impairments in bone stiffness (P=0.03) and failure load (P=0.04), she reported.

In other analyses, visceral fat was a negative predictor of both of these properties (stiffness, P=0.008, and failure load, P=0.01), as was total adipose tissue (P=0.02 and P=0.03, respectively).

Thigh muscle area had a positive correlation with stiffness and failure load, they found (P=0.05 and P=0.02, respectively).

"The more visceral fat you have, the lower the bone strength," Bredella said. "The more muscle mass you have, the stronger your bones are."

She calculated that the estimated fracture risk would be about 25% higher in men with lots of visceral fat compared with those who had less.

Bredella added that there was no association between age, BMI, or subcutaneous tissue and these mechanical properties of bone.

She concluded that the findings support the notion that visceral fat exerts detrimental effects on bone strength, and that visceral fat is not only a risk factor for heart disease and diabetes, but also for bone loss.

"There is hope that if you lose the fat, your bones will get better, but it's very hard to lose [visceral fat] selectively," she said. "We cannot determine where we gain the weight or lose it, so you just have to go for diet and exercise. There is no specific diet or specific exercise that targets the visceral fat, unfortunately."

Judy Yee, MD, vice chair of radiology at the University of California San Francisco, who moderated the session during which the findings were presented, said the study suggests that BMI may not be a useful tool for assessing fracture risk in general.

"You cannot rely on just BMI to determine your risk because it does not tell you the distribution of where that fat is," she said.

But she cautioned that this doesn't preclude BMI as a useful tool for risk assessment in other settings.

"It would be a first step because you need something that's easy to measure, that you can get to a large population inexpensively, and that is easy to do," Yee said. "It's a good initial screen, but individuals who have other risk factors should, in the future, get additional levels of evaluation outside of BMI."

The study was supported by grants from the National Institutes of Health.

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